1. Technical Field
The present invention relates to a display apparatus including a liquid crystal panel which displays an image and a plurality of light sources which irradiate the liquid crystal panel with light, and a display system.
2. Description of Related Art
Recently, the development of a liquid crystal display (LCD) having a three-dimensional (3D) display function for displaying a 3D image has been progressed. The 3D display function employs, for example, a frame sequential system using a liquid crystal shutter glasses (hereinafter, referred to as a glasses). The frame sequential system alternately displays an image for right eye (hereinafter, referred to as a right-eye image) and an image for left eye (hereinafter, referred to as a left-eye image) on a liquid crystal display in a time division manner, and blocks a sight of the left eye by the glasses during displaying the right-eye image, while blocking a sight of the right eye by the glasses during displaying the left-eye image. By repeating these display processing of the image and blocking processing by the glasses, the left and right eyes of a viewing user (viewer) may view the image different from each other, and due to a difference (parallax) between the right-eye image and the left-eye image, the user can perceive the image to be a stereoscopic image.
In the liquid crystal display employing the frame sequential system, it is important to suppress an occurrence of a phenomenon (a so-called crosstalk) that the right-eye image enters into the sight of the left eye, or the left-eye image enters into the sight of the right eye, in terms of improving display performance. As an effective technique for suppressing the occurrence of crosstalk, a backlight scanning technique, in which a backlight (light source) is divided into a plurality of regions and the backlight is turned on for each region, has been known in the art. By using the backlight scanning technique, when the backlight is turned on only in a latter period in which a response of the liquid crystal display element has been subsided within a period of displaying one image frame (within one frame period), it is possible to prevent an image of the next image frame (for example, left-eye image) from being entered into the image of the previous image frame (for example, right-eye image).
Hereinafter, processing of controlling the liquid crystal panel, the backlight and the glasses using the backlight scanning technique will be described.
FIG. 1 is a schematic view illustrating a relationship between the liquid crystal panel and the light source in the liquid crystal display. FIG. 1 illustrates a liquid crystal panel 90 as seen from a display surface side. The liquid crystal display illustrated in FIG. 1 is a light guide type (edge light type) liquid crystal display, and includes the liquid crystal panel 90, and light sources 91 to 96 which irradiate the liquid crystal panel 90 with light. In addition, the liquid crystal display includes a light guide plate (not illustrated) which is disposed on a back surface side (surface side opposite to the display surface) of the liquid crystal panel 90 to guide light from the light sources 91 to 96 to the liquid crystal panel 90. The liquid crystal panel 90 is configured to perform the display control of the image for each display region (first region, second region, . . . , and sixth region) which is divided into six, for example, in a longitudinal direction (vertical direction) and respectively has a strip shape. The light guide plate has a size substantially the same as the liquid crystal panel 90. The light sources 91 to 96 are provided at positions respectively facing both end surfaces of the light guide plate in a lengthwise direction (lateral direction) thereof, that is, positions respectively corresponding to two short sides of each display region of the liquid crystal panel 90. Thereby, the respective light sources 91 to 96 irradiate each display region of the liquid crystal panel 90 with light through the light guide plate.
FIG. 2 is a view for describing control processing for the liquid crystal panel 90, the light sources 91 to 96 and glasses. FIG. 2 illustrates a change in a display image and a change in values of current applied to the light sources 91 to 96 with the passage of time, in each display region (first region, second region, . . . , and sixth region) of the liquid crystal panel 90, and further illustrates a change in sight control by the glasses with the passage of time. Further, FIG. 2 illustrates a time axis (lateral axis) for showing the change in the display image, and a time axis (lateral axis) and current values (vertical axis) for showing the change in the values of current applied to the light source 91, only for the first region, and the axes are not illustrated for the other display regions. Further, a time axis (lateral axis) for showing the change in the sight control by the glasses is also not illustrated.
In an example illustrated in FIG. 2, displaying of signals included in the image frame (right-eye or left-eye image frame) in each display region is sequentially started with predetermined time-lags in an order of the first region, the second region, . . . , and the sixth region, and one image frame is displayed on the liquid crystal panel 90 as a whole. The signals included in the right-eye and left-eye image frames are alternately displayed in each display region. The respective light sources 91 to 96 are controlled so as to irradiate each display region with light during a latter period within a period in which each display region displays each signal in the one image frame. Specifically, the light sources 91 to 96 are turned on when a predetermined time t has elapsed after the displaying of the signal in the one image frame in the display region corresponding thereto is started, and are turned off when displaying of the signal in the next image frame is started. Herein, the predetermined time t is time considering the time (transient response time) until each liquid crystal display element reaches transmittance based on the signal to be displayed. In addition, the values of current applied to the respective light sources 91 to 96 are the same as each other and the respective light sources 91 to 96 irradiate light having the same luminance as each other.
The glasses, for example, while the signal in the left-eye image frame is displayed in the sixth region, block the sight of the right eye and open only the sight of the left eye, and while the signal in the right-eye image frame is displayed in the sixth region, block the sight of the left eye and open only the sight of the right eye.
In this way, within the display period of the one image frame, the backlight is turned on only in the period in which the response of the liquid crystal display element has been subsided, such that the occurrence of crosstalk is suppressed, and the display performance of liquid crystal displays is improved.
However, when performing the control processing as illustrated in FIG. 2, the light from the light sources 91 to 96 which have been turned on enters (is leaked) into the display region corresponding to the light sources 91 to 96 which have been turned off, such that the crosstalk may occur. For example, in a period in which the right-eye image frame is displayed in the first region among the period in which the sight of the left eye is opened by the glasses, the light from the lighting light sources 92 to 96 enters into the first region, respectively. In this case, under the condition in which the sight of the left eye is opened, the light from the light sources 92 to 96 enters into the first region which is displaying the right-eye image frame, and thereby a part of the right-eye image frame is viewed by the left eye. Similarly, when the sight of the left eye is opened, the light from the light sources 93 to 96 enters into the second region which is displaying the right-eye image frame, and thereby a part of the right-eye image frame is viewed by the left eye. The similar crosstalk also occurs in the third to fifth regions. Further, when the sight of the left eye is opened, only the left-eye image frame is displayed in the sixth region, thus the crosstalk does not occur in the sixth region. In this way, when displaying the image on the liquid crystal panel 90 by scanning each display region in the order of the first region, the second region, . . . , and the sixth region, the occurring crosstalk is more apparent toward an upper portion of the screen (first region).
In order to suppress the occurrence of the above-described crosstalk, it is conceivable that a light guide plate capable of exactly dividing light is used, or an appropriate pattern is formed on the light guide plate, so that each light from the light sources 91 to 96 does not leak to a region other than the display regions corresponding thereto.
In addition, Japanese Patent Application Laid-Open No. 2010-276928 proposes a technique in which the turn on time (lighting time) of the light sources corresponding to the respective regions of the liquid crystal panel does not overlap with each other, thereby suppressing the occurrence of the 3D crosstalk.